1. Field of the Invention
The present invention is concerned with the detection of the proximity of an object to one or more high voltage power lines and more particularly relates to a system and a method to detect proximity to high power alternating current electrical lines. The invention provides a means of signalling to the operator of heavy equipment in the environment of such lines of the danger of a portion of the equipment being too close to such high voltage electrical lines.
2. Description of Prior Art
Each year, an increasing number of workers are subjected to injuries, resulting in physical and psychological damage, from electrical shocks when an equipment that a person is operating or standing close to comes in contact with or too close to a high power electrical line. Such is often the case when a crane or a vehicle having a boom is operating near such lines. In order to try to reduce this danger, various proximity detection systems or devices have been developed and used. Such systems or devices utilize circuits which operate on the principle of the measurement of equipotential voltages. It is known that an electrical field builds up about electrical power lines and the intensity of such field decreases along equipotential lines. The voltage of the field is measured and increases as the measuring device is displaced closer and closer to the electrical power line, the maximum intensity of the voltage being achieved when the measuring antenna touches the line. In the detection circuits heretofore known, the equipotential voltage which is received by the antenna is measured and compared to a known value and all measured voltages that are greater than the known value cause an alarm to be activated.
One of the major disadvantages of such systems is that the voltage which is received by the antenna leans toward a limit value which is the line to ground voltage. Thus, in the presence of two electrical lines of different voltages, there is a risk of touching the line at the lowest voltage without activating the alarm. It is conceivable that the level of the voltage required to trigger the alarm of one of the lines, having the higher voltage, can be higher to the actual voltage on the other line. Also, it is pointed out that equipotential voltages are easily disturbed by neighboring metallic structures (i.e., steel towers). To all these inconveniences, there is also the difficulty of measuring equipotential voltages due to the requirement of very high impedance circuits.